This application claims benefit of Japanese Application No. 2001-3439 filed in Japan on Jan. 11, 2001, the contents of which are incorporated by this reference.
The present invention relates generally to a zoom optical system used with image pickup devices, and more particularly to a zoom optical system for use with photographic cameras, especially lens shutter cameras.
Cameras having zoom lenses are now popular for recent lens shutter cameras, and there are growing demands for cameras equipped with a compact phototaking lens having an increased zoom ratio.
Generally, a zoom optical system having a zoom ratio of about 2 to 3 is constructed in the form of a two-group one consisting of, in order from its object side, a lens group having positive refracting power and a lens group having negative refracting power, and a zoom optical system having a zoom ratio of about 3 to 4.5 is set up in the form of a three-group one consisting of, in order from its object side, a lens group having positive refracting power, a lens group having positive refracting power and a lens group having negative refracting power.
In general, two-group zoom arrangements are used especially for lens shutter cameras targeted at low cost and compactness, because of comprising a simple mechanical mechanism with reduced sensitivities of the adjacent lens groups to decentration.
Some two-group zoom lens systems having a zoom ratio of about 3 are generally designed with an angle of view of about 60xc2x0 at the wide-angle end. On account of growing needs for scenic shots taken at wider-angle ends, which are a reflection of recent going-abroad booms, and for lens shutter cameras with wide-angle zoom lenses at oversea markets, however, there is an increasing demand for two-group zoom lenses having an angle of view of about 70xc2x0 or greater at the wide-angle ends and having a zoom ratio of about 3.
With zoom lenses having a zoom ratio of about 3 while maintaining an angle of view of about 70xc2x0 or greater at the wide-angle ends, however, it is difficult to maintain image-formation capability at the telephoto ends.
Lens arrangements so far proposed to overcome such problems are disclosed in JP-A""s 11-14903, 2000-28921 and 2000-137163.
However, the lens arrangements set forth in JP-A""s 11-14903 and 2000-137163 have a zoom ratio of as low as 2.8 although the angle of view at the wide-angle ends is of the order of 70xc2x0 or greater. The lens arrangement of JP-A 2000-28921, too, has an zoom ratio of at most 3 although the angle of view at the wide-angle end is 70xc2x0 or greater.
In view of such states of the prior art, an object of the invention is provide a zoom optical system having a wider angle of view at the wide-angle end and an increased zoom ratio, especially a compact two-group zoom optical system capable of maintaining satisfactory image-formation capability all over the zooming range, albeit having an angle of view of 70xc2x0 or greater at the wide-angle end and a zoom ratio of 3 or greater.
According to the first aspect of the invention designed to achieve this object, there is provided a zoom lens optical system having a zoom ratio of 3 or greater and comprising, in order from an object side thereof, a first lens group having positive refracting power and a second lens group having negative refracting power in which, for zooming from a wide-angle end to a telephoto end of the zoom lens optical system, the respective lens groups move toward the object side with a decreasing spacing between the first lens group and the second lens group, wherein:
the first lens group consists of, in order from an object side thereof, a first lens unit (U1) having negative refracting power, a second lens unit (U2) having positive refracting power and a third lens group (U3) having positive refracting power wherein each lens unit consists of a single lens or a cemented lens, and satisfies the following condition:
0.35 less than fG1/f12 less than 1.5xe2x80x83xe2x80x83(1)
where fG1 is the focal length of the first lens group, and f12 is the focal length of the second lens unit.
According to the second aspect of the invention, there is provided a zoom lens optical system comprising, in order from an object side thereof, a first lens group having positive refracting power and a second lens group having negative refracting power in which, for zooming from a wide-angle end to a telephoto end of the zoom lens optical system, the respective lens groups move toward the object side with a decreasing spacing between the first lens group and the second lens group, wherein:
the first lens group consists of, in order from an object side thereof, a first lens unit (U1) having negative refracting power, a second lens unit (U2) having positive refracting power and a third lens unit (U3) having positive refracting power wherein each lens unit consists of a single lens or a doublet, while the following conditions are satisfied:
0.8 less than |fG1/f11| less than 3xe2x80x83xe2x80x83(2)
0.35 less than fG1/f12 less than 3xe2x80x83xe2x80x83(3)
0.8 less than fG1/f13 less than 3xe2x80x83xe2x80x83(4)
where fG1 is the focal length of the first lens group, f11 is the focal length of the first lens unit, f12 is the focal length of the second lens unit, and f13 is the focal length of the third lens unit.
Preferably in the first or second aspect of the invention, the surface, located nearest to the object side, of the first lens unit in the first lens group is concave on the object side.
Preferably in the first or second aspect of the invention, the second lens unit in the first lens group is a doublet consisting of, in order from an object side thereof, a negative meniscus lens convex on an object side thereof and a positive lens.
Preferably, the second lens unit in the first lens group satisfies the following condition:
30 less than xcexd12Pxe2x88x92xcexd12N less than 50xe2x80x83xe2x80x83(5)
where xcexd12P is the Abbe""s number of the positive lens in the second lens unit, and xcexd12N is the Abbe""s number of the negative lens in the second lens unit.
Preferably in the first, second and subsequent aspects of the invention, the third lens unit in the first lens group comprises at least one aspheric surface that satisfies the following condition:
0 less than |xcex94A/ST| less than 4.5xc3x9710xe2x88x922xe2x80x83xe2x80x83(6)
where xcex94A is the amount of the aspheric surface at a height from an optical system to 0.8 times the radius of an aperture stop, and ST is the radius of the aperture stop at a telephoto end.
According to the third aspect of the invention, there is provided a zoom lens optical system comprising, in order from an object side thereof, a first lens group having positive refracting power and a second lens group having negative refracting power in which, for zooming from a wide-angle end to a telephoto end of the zoom lens optical system, the respective lens groups move toward the object side with a decreasing spacing between the first lens group and the second lens group, wherein:
the first lens group consists of, in order from an object side thereof, a first lens unit (U1) having negative refracting power, a second lens unit (U2) having positive refracting power and a third lens unit (U3) having positive refracting power wherein the first lens unit is a doublet consisting of a negative lens and a positive lens in order from an object side thereof, and the second lens unit is a doublet consisting of a negative lens and a positive lens in order from an object side thereof.
According to the fourth aspect of the invention, there is provided a zoom lens optical system having a zoom ratio of 3 or greater and comprising, in order from an object side thereof, a first lens group having positive refracting power and a second lens group having negative refracting power in which, for zooming from a wide-angle end to a telephoto end of the zoom lens optical system, the respective lens groups move toward the object side with a decreasing spacing between the first lens group and the second lens group, wherein:
the first lens group consists of, in order from an object side thereof, a first lens unit (U1) that has negative refracting power and in which the surface located nearest to an object side thereof is concave on the object side, a second lens unit (U2) having positive refracting power, a third lens unit (U3) having negative refracting power and a fourth lens unit (U4) having positive refracting power, wherein each lens unit in the first lens group consists of a single lens or a doublet.
According to the fifth aspect of the invention, there is provided a zoom lens optical system comprising, in order from an object side thereof, a first lens group having positive refracting power and a second lens group having negative refracting power in which, for zooming from a wide-angle end to a telephoto end of the zoom lens optical system, the respective lens groups move toward the object side with a decreasing spacing between the first lens group and the second lens group, wherein:
the first lens group consists of, in order from an object side thereof, a first lens unit (U1) that has negative refracting power and in which the surface located nearest to an object side thereof is concave on the object side, a second lens unit (U2) having positive refracting power, a third lens unit (U3) having negative or positive refracting power and a fourth lens unit (U4) having positive refracting power, wherein the respective lens units in the first lens group consist of a single lens or a doublet and satisfy the following conditions:
0.5 less than |fG1/f11| less than 3xe2x80x83xe2x80x83(7)
xe2x88x920.4 less than fG1/f13 less than 0.1xe2x80x83xe2x80x83(8)
where fG1 is the focal length of the first lens group, f11 is the focal length of the first lens unit, and f13 is the focal length of the third lens unit.
Preferably in the fourth or fifth aspect of the invention, at least one surface of the second or fourth lens unit in the first lens group is defined by an aspheric surface.
According to the sixth aspect of the invention, there is provided a zoom lens optical system comprising, in order from an object side thereof, a first lens group having positive refracting power and a second lens group having negative refracting power in which, for zooming from a wide-angle end to a telephoto end of the zoom lens optical system, the respective lens groups move toward the object side with a decreasing spacing between the first lens group and the second lens group, wherein:
the first lens group consists of, in order from an object side thereof, a first lens unit (U1) that has negative refracting power and in which the surface located nearest to an object side thereof is concave on the object side, a second lens unit (U2) that has positive refracting power, comprises at least one aspheric surface and is formed of a plastic material, a third lens unit (U3) having positive refracting power and a fourth lens unit (U4) having positive refracting power, wherein the respective lens units in the first lens group consist of a single lens or a doublet and satisfy the following conditions:
200xc3x9710xe2x88x925 less than |xcex94NP|xe2x80x83xe2x80x83(9)
0 less than |fG1/f12| less than 0.25xe2x80x83xe2x80x83(10)
0 less than fG1/f13 less than 0.5xe2x80x83xe2x80x83(11)
where xcex94NP is the amount of change in the refractive index (nd) of the plastic material with respect to a d-line wavelength of 587.56 nm due to a temperature change of xe2x88x9210xc2x0 C. to 40xc2x0 C., fG1 is the focal length of the first lens group, f12 is the focal length of the second lens unit, and f13 is the focal length of the third lens unit.
According to the seventh aspect of the invention, there is provided a zoom lens optical system comprising, in order from an object side thereof, a first lens group having positive refracting power and a second lens group having negative refracting power in which, for zooming from a wide-angle end to a telephoto end of the zoom lens optical system, the respective lens groups move toward the object side with a decreasing spacing between the first lens group and the second lens group, wherein:
the first lens group consists of, in order from an object side thereof, a first lens unit (U1) that has negative refracting power and in which the surface located nearest to an object side thereof is concave on the object side, a second lens unit (U2) that has positive refracting power and is in a meniscus form convex on an object side thereof, a third lens unit (U3) that is a doublet consisting of a negative lens and a positive lens in order from an object side thereof and has negative or positive refracting power and a fourth lens unit (U4) having positive refracting power.
Preferably in any one of the zoom optical systems of the invention, the zoom ratio should be as high as 3 or greater, and especially as high as 3.3 or greater.
Preferably in any one of the zoom optical systems of the invention, the angle of view at the wide-angle end should be 70xc2x0 or greater.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.